<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>css属性</title>
    <style>
        div{
            border:1px solid red;
        }
        div1{
            width: 100px;
            height: 100px;
        }
        div2{
            width: 400px;
            height: 400px;
            padding: 50px;
            box-sizing: border-box;
        }

    </style>
</head>
<body>
    <div class="div2">
        <div class="div1"></div>
    </div>
</body>
</html>